The following invention relates to electronic spindle motors of the type used in disk drives and in particular relates to improvements in fluid bearings for such motors.
Electric spindle motors of the type used in disk drives conventionally rely on ball bearings to support a rotary member, such as a rotating hub, on a stationary member, such as a shaft. Ball bearings are wear parts and in time friction will cause failure of the motor. In addition, ball bearings create debris in the form of dust or fine particles that can find their way into "clean" chambers housing the rotary magnetic disks which are driven by the motor. The mechanical friction inherent in ball bearings also generates heat and noise, both of which are undesirable in a disk drive motor.
Fluid bearings represent a considerable improvement over conventional ball bearings in spindle drive motors. Fluid or "hydrodynamic" bearings are shown in Titcomb, et al., U.S. Pats. Nos. 5,112,142, 4,795,275, and 5,067,528. Other types of fluid bearings are shown in Shinohara U.S. Pat. No. 4,445,793 and Anderson, et al., U.S. Pat. No. 4,726,693.
Of paramount importance in the design of fluid bearings is the integrity of the seal formed by the fluid. If the seal breaks, the fluid runs out of the bearing, rendering the motor inoperative. Seals can be formed by capillary action of the fluid which creates a surface tension seal. Such a seal is shown in the aforementioned Titcomb, et al., U.S..Pat. No. 5,112,142. In the Titcomb patent capillary seals are created by tapering, in the axial direction, one of the two surfaces that defines the capillary gap between rotating and non-rotating parts where the bearing or lubricating fluid is located. Such capillary seals are formed in the radial capillary gaps that separate, for example, a stationary shaft and a rotating sleeve.
A problem unique to fluid bearings is the possible rupturing of the surface tension seal which would allow the bearing fluid to escape. This can be caused by changes in atmospheric pressure that are associated with changes in altitude and other environmental factors. It would therefore be desirable to enhance the integrity of the seal for such fluid bearings without incurring the cost of increasing the size, especially the axial length, of the motor. Obviously the longer the taper that creates the capillary action, the better the integrity of the surface tension seal. However, spindle motors of the type used in disk drives are becoming increasingly smaller with the result that surface area, especially in the axial direction, is at a premium.